Discospondylitis
Infection of the Spinal Vertebrae and Intervertebral Discs

Discospondylitis is an infection of the spinal vertebrae and intervertebral discs. It has been referred to as a form of arthritis of the spine with narrowing of the involved disc spaces. It is a form of vertebral osteomyelitis (bone infection) but it can be differentiated from this general classification by the involvement of the intervertebral discs, adjacent vertebral bony endplates, and vertebral bodies (see Fig.1).

The most common clinical signs of affected dogs include intense spinal pain and neurologic weakness manifested as slowly progressive incoordination of the limbs caudal to the site of the lesion. As swelling, inflammation, bony proliferation, and spinal cord compression increase, the dog becomes much more painful. Although there does not appear to be any breed predisposition, one report indicates a marked prevalence of the syndrome in large dogs. The thoracolumbar (mid-back) area accounts for the greatest number of discospondylytic lesions.

The mechanisms of infection include the following:

• Hematogenous (blood borne)
• Secondary to adjacent infection (i.e. foxtail migration or other foreign bodies)

Hematogenous Discopondylitis

Septicemia is defined as a blood infection with circulating bacterial or fungal organisms. This could be from an abscessed tooth, bladder infection, wound, immune disorder, or from a debilitating disease. The infectious organisms circulating in the bloodstream find their way to the soft tissues adjacent to the vertebrae. Small abscesses may develop. Reactive bone spurs appear, involving the vertebral bodies, and subsequently spread to the discs between two vertebrae. In some cases, the body kills the infectious agents and fuses the vertebrae. However, most affected dogs require treatment for pain and neurologic dysfunction before there is time for this process to occur (see Fig. 2).

Discospondylitis Secondary to Adjacent Infection

Foreign bodies (i.e. bullets and foxtails) are the most common sources of reported cases of discospondylitis which result from adjacent tissue infection. The pathologic process is not unlike that previously described. The extensive soft tissue infection invades the adjacent bony structures and, when in the area of the disc space, results in discospondylitis.

Management and Treatment

Treatment of discospondylitis in dogs follows guidelines similar to those used in man. Long term antibiotic therapy (four to six weeks) is the most common treatment. This treatment is usually aimed at the most commonly isolated microorganism: Staphylococcus aureus. When no response to antibiotic therapy is seen, or when recurrence is a problem, surgical biopsy, bacterial culture, and antibiotic sensitivity testing are needed. When severe neurologic deficits exist, they are due to pressure on the spinal cord. Antibiotics in conjunction with surgery have proven very successful. Ultimately, joint fusion must be achieved either with antibiotic therapy alone or in combination with spinal surgery to maintain immobilization and allow healing by bony consolidation. In most cases, progression of bony healing and joint fusion become evident on x-rays within a few weeks. The soft tissue reaction subsides as the vertebrae and discs return to a more normal appearance following bony fusion of the involved areas.